Infections of the eye can be clinically classified according to the anatomical compartment harboring and consequently affected by the infection. There are many organisms which can cause ocular infections and are in detail described in “Principles and Practice of Infectious Diseases, 6th Edition, Gerald Mandell et al (Eds) Elsevier Churchill Livingston, pp 1387-1418 (2005) the disclosure of which is incorporated by reference here.
Ophthalmic infections can be classified into the following categories based clinician's initial diagnosis:                1. External ocular Infections such as Keratitis and Conjunctivitis        2. Infectious Endophthalmitis        3. Uveitis        4. Retinitis        
There are many external ocular infections caused by several bacteria and fungi. The fact that conjunctiva and cornea harbor many non-pathogenic bacteria and fungi as passengers due to the exposure to the environment vitiates detection of specific pathogens (bacteria and fungi) in a scraping or a swab taken from conjunctiva or cornea. In the presence of suppuration or ulceration with pus, clinicians make provisional diagnosis of bacterial infection and treat patients with broad-spectrum antibiotics applied topically. However crucial infections difficult to diagnose but eminently curable are:
Herpes simplex (causing Keratitis)                Adenoviral kerato-conjunctivitis (some times caused in epidemic proportions)        Chlamydia trachomatis (causing follicular conjunctivitis leading to trachoma and adult inclusion conjunctivitis)        Varicella conjunctivitis (also called Herpes zoster conjunctivitis)        Rapidly growing Mycobacteria such as M. chelonae and M. fortuitum (cause infections after LASIK, a surgery conducted in order to reduce the refractive errors)        
Infectious Endophthalmitis can be caused generally by a                Gram-positive bacteria        Gram-negative bacteria        Anaerobic organisms viz. Propionibacterium acnes         Fungi.        
Quite commonly the infection is post operative and spreads very fast resulting in blindness. Most important information required for treatment is whether the causative agent is bacterium or fungus and if it is bacterium whether it is aerobic or anaerobic. Endogenous infections caused by haematogenous spread are rare.
Uveitis is generally caused by                Mycobacterium tuberculosis,         M. chelonae,         M. fortuitum,         Toxoplasma gondii         
Retinitis is generally seen in immuno-compromised individuals and is caused by                Cytomegalovirus        Herpes simplex virus        Varicella zoster virus        
Significant loss of vision occurs in all these patients and early and timely diagnosis of these organisms is an important component in prevention of blindness across the globe. The actual incidence of these infections may be relatively higher in developing nations. Many diagnostic techniques are for the diagnosis of eye infections as detailed in Prior Art.
Central Nervous system infections can be classified in to the following categories:
Acute pyogenic meningitis: generally seen in children and is caused by organisms such as                Haemophilus influenza,        Neisseria meningitides and        Streptococcus pneumoniae.         
Bacterial cultures or smear microscopy of the Cerebro-Spinal Fluid (CSF) sediments lack sensitivity. An additional complicating factor is that prior treatment of the patient with antibiotics can lead to a false-negative result of both gram-stain and culture from CSF. For these reasons, physicians are hesitant to rely on culture results and will opt to complete a full 10-14 day course of intravenous antibiotics, which in the majority of cases is not necessary. Once partially treated, the cases are indistinguishable from chronic meningitis caused by.                Mycobacterium tuberculosis         Various fungi        Viral encephalitis caused by a series of therapeutically amenable viruses viz., HSV, CMV and VZV.        
Encephalitis generally caused by a variety of viruses both endemic and epidemic. However, Herpes simplex, Cytomegaloviruses and Varicella zoster are the viruses for which specific antiviral therapy is available. Other treatable encephalitic agent is Toxoplasma gondii. 